Bellows-type seals are commonly employed for sealing axially movable valve members in axially movable plug or gate valves. Such bellows-type seals are entirely successful in such valves, in that the bellows-type seal is subjected to limited axial forces only, such forces being well within the handling capability of the selected bellows-type seal, those forces acting exclusively in directions axially of the bellows-type seal, and in the absence of bending or torsional forces applied to the bellows-type seal.
Such bellows-type seals also have been employed in the valve actuators of rotary-type valves, such as rotary plug valves, ball valves or butterfly valves. An example of such a rotary valve is to be found in Tremblay, U.S. Pat. No. 4,468,002, issued Aug. 28th, 1984. In the construction of that valve, a bearing, of necessity, must be provided between the rotary valve actuator and the bellows seal, in order to permit rotary movement of the valve actuator relative to the rotationally fixed bellows seal, the bellows seal itself being incapable of rotary movement. In the construction of this patent, the bearing is provided by a closed cap attached to one end of the bellows seal, the cap providing a bearing member that is interposed between the valve actuator and a valve actuating stem. The cap, upon actuation of the valve actuator, is caused to move along an orbital path, this in turn resulting in axial bending stresses being produced in the bellows-type seal, and, additionally, the imposition on the bellows-type seal of torsional forces arising from the frictional engagement of the bearing cap with the respective valve actuator and valve actuating spindle.
Such bending and torsional forces are objectionable, in that they promote fatigue failure of the bellows-type seal, which could have disastrous consequences to persons in the vicinity of the valve.